Humanity is 17 million tons (15 million metric tons) overweight, according to a study that calculates the adult portion of the human race's collective weight at 316 million tons (287 million metric tons).

That's the equivalent of about 170 military aircraft carriers of extra weight. Or in people weight, it's like having an extra 242 million people of average body mass on the planet.

This is more than just an attempt to make the human race feel uncomfortable about its waistline; looking at the collective mass of humanity can improve understanding of the effects of population growth, contends a team of European researchers.

"[United Nations] world population projections suggest that by 2050 there could be an additional 2.3 billion people," they write in research published online Sunday (June 17) in the journal BMC Public Health. "The ecological implications of rising population numbers will be exacerbated by increases in average body mass." [7 (Billion) Population Milestones]

The argument is simple. More body mass takes more energy to maintain and move; therefore as someone's weight goes up, so do the calories they need to exist. This means increases in population counts don't tell the whole story when it comes to demand for resources, according to the authors.

"Although the largest increase in population numbers is expected in Asia and sub-Saharan Africa, our results suggest that population increases in the USA will carry more weight than would be implied by numbers alone," they write.

The United States ranked at the top of the "Heaviest 10" category, while the "Lightest 10" list is composed entirely of African and Asian nations. For example, North America has 6 percent of the world population but 34 percent of biomass due to obesity. Meanwhile, Asia has 61 percent of the world population but just 13 percent of biomass due to obesity. [List of heaviest and lightest nations]

Using data from around the world for 2005, researchers used body mass indexes (BMI, or a measure of body fatness) and height distributions to estimate average adult body mass. They then multiplied these results by population size to get a total mass, referred to as biomass. They evaluated body mass using BMI thresholds of greater than 25 for overweight and greater than 30 for obese. The collective mass of the adult population in 2005 due to obesity was 3.9 million tons (3.5 million metric tons), they calculated.

Globally, average body mass globally for an individual was calculated at 137 pounds (62 kilograms).

"Our scenarios suggest that global trends of increasing body mass will have important resource implications and that unchecked, increasing BMI could have the same implications for world energy requirements as an extra 473 million people," they write. "Tackling population fatness may be critical to world food security and ecological sustainability."